To show the difference:
mintest(X, Y, Min) :-
( X @=< Y, !,
Min = X
; Min = Y
).
mintest(_X, _Y, strawberries_and_cream).
?- mintest(1, 2, Min).
Min = 1.
Vs:
mintest(X, Y, Min) :-
( X @=< Y
-> Min = X
; Min = Y
).
mintest(_X, _Y, strawberries_and_cream).
?- mintest(1, 2, Min).
Min = 1 ;
Min = strawberries_and_cream.
(Edit: moved ->
to its standard placement)