?- S = (tab/field = 2), display(S), S =.. [Op, L, R], Result =.. [Op, replaced, R].
=(/(tab,field),2)
S = (tab/field=2),
Op = (=),
L = tab/field,
R = 2,
Result = (replaced=2).
?- S = (+field > 2), display(S), S =.. [Op, L, R], Result =.. [Op, replaced, R].
>(+(field),2)
S = (+field>2),
Op = (>),
L = +field,
R = 2,
Result = (replaced>2).