Added verified setInTo function modifier.

Fun/Operations.lidr

 > module Fun.Operations
 
+> import Basic.Properties
+
 
 > %default total
 > %access public export
@@ -22,3 +24,24 @@
 > modifyFun f a b a' = if a' == a then b else f a'
 
 
+> |||
+> setInTo : {A : Type} -> {B : A -> Type} -> DecEq A =>
+>           (f : (a : A) -> B a) -> (a : A) -> B a -> ((a : A) -> B a)
+> setInTo f a b a' with (decEq a a')
+>   | (Yes prf)    =  replace prf b
+>   | (No contra)  =  f a'
+
+> setInToSpec1 : {A : Type} -> {B : A -> Type} -> DecEq A =>
+>           (f : (a : A) -> B a) -> (a : A) -> (b : B a) -> 
+>           setInTo f a b a = b
+> setInToSpec1 f a b with (decEq a a)
+>   | (Yes prf)    =  replaceLemma prf b
+>   | (No contra)  =  void (contra Refl)
+
+> setInToSpec2 : {A : Type} -> {B : A -> Type} -> DecEq A =>
+>           (f : (a : A) -> B a) -> (a : A) -> (b : B a) -> 
+>           (a' : A) -> Not (a = a') -> setInTo f a b a' = f a'
+> setInToSpec2 f a b a' contra' with (decEq a a')
+>   | (Yes prf)    =  void (contra' prf)
+>   | (No contra)  =  Refl
+