prolog syntax problem

Question

I can't distinguish these symbols:

= and =:=

\= and =\=

[X,Y] and [X|Y]

What’s the difference ?

Answer 1

For the comparison operators (=, =:=, \=, =\=):

• = succeeds if the terms unify (basically, if they're bound together)
• =:= succeeds if the values of the terms are equal (should be equivalent to = if you're dealing with numbers, I believe)
• \= is the negation of =
• =\= is the negation of =:=

For more info about these operators and more, see this page.

For the list operators, [X|Y] is a way to refer to a list where X is the first element and Y is the list of the remaining elements. [X, Y] is just another way to refer to this, but it limits Y to being a single element, instead of possibly a whole list of them. For more info, see this section of the same page.