Attributes[Pivot] = {HoldAll}
Pivot/: Pivot[a_, i_, j_] := 
   (a[[i]] = a[[i]]/a[[i,j]]; For[k = If[i == 1, 2, 1], k <= Length[a], 
      If[++k == i, ++k, k], a[[k]] = a[[k]] - a[[i]]*a[[k,j]]];
      MatrixForm[a])