Convenience

P$\bf ,$Q
,/2 (I) P and then Q.

P$\bf ;$Q
;/2 (I) P or Q.

true
true/0 (I) Always succeeds.

X$\bf =$Y
=/2 (I) Defined as if by the clause ``Z=Z'', i.e. X and Y are unified.

X$\bf\backslash\,=$Y
\ =/2 (I) Succeeds if X and Y are not unifiable, fails if X and Y are unifiable. It is thus equivalent to not(X = Y), but is significantly more efficient.

X$\bf ?=$Y
?=/2 (I) Succeeds if X and Y are unifiable and fails if they are not, but does not instantiate any variables. Thus, it tests whether X and Y are unifiable. Equivalent to $\em not$($\em not$(X = Y)), but is significantly more efficient.