lispdoc  results for substif 
(substif new test tree &key key)  Function: Substitutes new for subtrees for which test is true.

Mentioned in: CLtL2  15.4. Substitution of Expressions HyperSpec  Function SUBST, SUBSTIF, SUBSTIFNOT, NSUBST, NSUBSTIF, NSUBSTIFNOT PCL  trees  
(substifnot new test tree &key key)  Function: Substitutes new for subtrees for which test is false.

Mentioned in: CLtL2  15.4. Substitution of Expressions HyperSpec  Function SUBST, SUBSTIF, SUBSTIFNOT, NSUBST, NSUBSTIF, NSUBSTIFNOT PCL  trees  
By Bill Moorier 