select/4

Availability::- use_module(library(lists)).(can be autoloaded)

[nondet]select(?X, ?XList, ?Y, ?YList)

Select from two lists at the same position. True if XList is unifiable with YList apart a single element at the same position that is unified with X in XList and with Y in YList. A typical use for this predicate is to replace an element, as shown in the example below. All possible substitutions are performed on backtracking.

?- select(b, [a,b,c,b], 2, X).
X = [a, 2, c, b] ;
X = [a, b, c, 2] ;
false.

See also: selectchk/4 provides a semidet version.