Hi,
Not sure about Thread[], but see documentation for Listable
SetAttributes[blafun2, Listable] ;
blafun2[a_, b_, c_] := If[a + b + c > 0, a + b + c, 2] ;
blafun2[a, b, {c1, c2, c3}]
ClearAttributes[blafun2, Listable] ;
(* {If[a + b + c1 > 0, a + b + c1, 2], If[a + b + c2 > 0, a + b + c2, 2], If[a + b + c3 > 0, a + b + c3, 2]} *)
I.M.
