.Open Syntax of the Logic Programming language Prolog
. Introduction
The syntax of Prolog is deceptively simple.  The User inputs a
series of predicates that have three different meanings - facts
to be stored, goals to be searched for(queries), or commands(directives)
which do one thing.  There is also a special kind of rule called
a clause which defines conditions underwhich a fact can be true.
. Input to Interpretter
	goal::= predicate"." -- input to intpereter at the "?-" prompt.

	command::=":-" predicate"." .
Notice the periods and other punctuators!

. Basics
	fact::=clause ".",
	clause::=predicate":-"predicate.
	query::=goal.
. Predicates
	predicate::=structure,
. Structures
A structure looks like an expression in an imperative language
but it is only evaluated onder special ccircumstances.  Most of the
time it is stored and treated as if it was a tree structure.

	structure::=prefix argument | argument postfix | argument infix argument | functor"(" arguments ")" | functor | array.

Note that "," and ";" are also infix operators.
	array ::= "[]" | "[" arguments "]" | "[" arguments "|" arguments "]",
	arguments::= argument | argument "," arguments,
	argument::=constant | variable | structure,
	constant::= number | string | atom | byte_array,
	atom::=lower_case_word #("_" word),
	string::= "'" #char "'",
	byte_array::= double_quote #char double_quote,
	variable::= ("_"|"A".."Z")#(letters|digits|"_").
	functor::=atom.

A functor is a non-numeric constant that is written as if it was a
function.   It is called a funct_or because it is just a formula and
may never be evaluated - it is just a way to label the kind of
structure involved. For example here are two facts that might appear
in a Prolog database and/or program:
.Box
 married(X, wife(X)).
	married(husband(X),X).
.Close.Box
However we never have to define what it means to evaluate
.Box
 wife(X)
 husband(X).
.Close.Box
Prolog will automatically generate constants to fit the structure:
.As_is 	?- married(dick,Y).
.As_is 	Y= wife(dick),
for us.  But `wife(dick)`
will not match wife(X) with any structure that doesn't have 'wife' in front:
.As_is 	married(dick, tricia)?
.As_is 	*No
Clever programming of special predicates (`para-modulation`) can 
express out intuitive understanding that
.Box
 X = wife(Y) if and only if Y=husband(X).
.Close.Box
But this goes beyond this simple introduction.

Some commands interpret some of the structures in special ways.  For example,
A predicate input as a fact is stored as piece of data, but input as a
command or goal it becomes a call to a procedure.  A clause is also
stored by Prolog but then it can act as a subprogram that
can be called as a command, or as part of another command.

 
Associated with each functor in a compound term is the number of 
arguments it has.  This is called its arity([sic] "arity"). An atom can 
different definitions for different arities.  

. Logic Programs 
program ::= sentence  #( ". " sentences),
 
sentence ::= head sentence_body,
 
sentence_head ::= ( | goal),
 
sentence_body ::= #goal,
 
non_unit_clause ::= head_goal ":-" ( | #goal),
 
goal ::=compund_term, 

unit_clause ::= head_goal,
 
.Close Syntax
.Open Quick reference lists
. Punctuation
comma(and), semicolon(or), exclamation(cut),-->(produces).
. Relations
<, =, =.., =:=, =<, ==, =@=, =\=, >, >=, @<, @=<, @>, @>=, \+, \=, \==, \=@=,
. Predicates
abolish, abort, absolute_file_name, absolute_file_name, access_file, append, append, apply, apropos, arg, arithmetic_function, assert, assert, asserta, asserta, assertz, assertz, at_halt, at_initialization, atom, atom_char, atom_chars, atom_length, atom_to_term, atomic, autoload,

bagof, between, block, break,

call, call, call_dll_function, call_shared_object_function, character_count, chdir, checklist, clause, clause, clause_property, close, close_dde_conversation, close_dll, close_shared_object, compare, compiling, compound, concat, concat_atom, consult, context_module, convert_time, copy_term, current_arithmetic_function, current_atom, current_flag, current_foreign_library, current_functor, current_input, current_key, current_module, current_module, current_op, current_output, current_predicate, current_stream,

dde_current_connection, dde_current_service, dde_execute, dde_register_service, dde_request, dde_unregister_service, debug, debugging, default_module, delete, delete_file, discontiguous, display, displayq, dwim_match, dwim_predicate, dynamic,

ed, ed, edit, edit, edit_source, ensure_loaded, erase, exception, exists_directory, exists_file, exit, expand_file_name, expand_file_search_path, expand_term, explain, explain, export, export_list,

fail, feature, file_base_name, file_directory_name, file_search_path, fileerrors, findall, flag, flatten, float, flush, flush_output, forall, foreign_file, format, free_variables, functor, 

garbage_collect, gensym, get, get, get0, get_single_char, get_time, getenv, ground,

halt, hash_term, help, history_depth,

ignore, import, index, initialization, int_to_atom, integer, intersection, is, is_absolute_file_name, is_list, is_set,

keysort,

last, leash, length, library_directory, limit_stack, line_count, line_position, list_to_set, listing, load_foreign, load_foreign_library,

make, make_fat_filemap, make_library_index, maplist, member, merge, merge_set, module, module_transparent, msort, multifile,

name, nl, nodebug, nonvar, noprotocol, nospy, nospyall, not, notrace, nth0, nth1, nth_clause, number, number_chars, numbervars,

once, op, open, open_dde_conversation, open_null_stream, open_shared_object,

phrase, please, plus, portray, portray_clause, predicate_property, predsort, preprocessor, print, profile, profile_count, profiler, prolog, prolog_current_frame, prolog_frame_attribute, prolog_load_context, prolog_skip_level, prolog_to_os_filename, prolog_trace_interception, prompt1, prompt, proper_list,
protocol, protocola, protocolling, put,

qcompile, qload, qsave_program, qsave_program,

read, read_clause, read_history, read_link, read_variables, recorda, recorded, recordz, redefine_system_predicate, rename_file, repeat, require, reset_profiler, restore, retract, retractall, reverse,

same_file, save, save_program, save_program, see, seeing, seen, select, set_feature, set_input, set_output, set_tty, setarg, setenv, setof, sformat, shell, show_profile, sleep, sort, source_file, source_location, spy, stack_parameter, statistics, stream_position, string, string_length, string_to_atom, string_to_list, style_check, sublist, subset, substring, subtract, succ, swritef,

tab, tell, telling, term_expansion, term_to_atom, time, time_file, tmp_file, told, trace, tracing, trim_stacks, true, tty_get_capability, tty_goto, tty_put, ttyflush,

union, unknown, unload_foreign_library, unsetenv, use_module, use_module,

var, visible, volatile

wait_for_input, wildcard_match, write, write_ln, writef, writeq,
. Arithmetic
*, **, +, -, -, /, //, /\, <<, >>, 'C', \, \/, ^,

abs, acos, asin, atan, atan, ceil, ceiling, cos, cputime, e, exp, float, float_fractional_part, float_integer_part, floor, integer, log, log10, max, min, mod, random, rem, round, truncate, pi, sign, sin, sqrt, tan, xor,
. Operators
discontiguous, dynamic, module_transparent, multifile, volatile, initialization,
:-, ?-, -->, :-,
.Close Quick reference lists 
. See also
.See http://www/dick/samples/comp.ascii.html
.See http://www/cs620/lab/sum.html