is mentioned by

Thm* a:array(T), j,i:|a|, v:T. a[i:=v][j] ~ if j=i v else a[j] fi	[array-update-select]
Thm* L: List, i,j:||L||. 0 < L[i] L[i--][j] = if j=i L[j]-1 else L[j] fi	[list-dec-select]
Def a[i:=v] == < |a|,j.if j=i v else a[j] fi >	[array-update]
Def L[i--] == mklist(||L||;j.if j=i L[j]-1 else L[j] fi)	[list-dec]

In prior sections: bool 1 sqequal 1 prog 1 mb nat graph 1 1 int 2 num thy 1 mb basic

Try larger context: Graphs