Leontief Function

Clear[a1, a2, x1, x2, Leontief]; 
a1 = 1
a2 = 1

Leontief = Min[a1*x1, a2*x2]

Plot3D[Leontief, {x1, 0, 1}, {x2, 0, 1}]

ContourPlot[Leontief, {x1, 0, 1}, {x2, 0, 1}]