These are answers submitted by Markiyan Hirnyk

This can be done in Maple 2015 as follows (see ?PolyhedralSets for info).

with(PolyhedralSets):

P := PolyhedralSet([p0 <= 60, -p0+p1 >= 4, -p0+p2 >= 5, -p0+p3 >= -12, p0-p2 >= -33, p1-p2 >= -36, p2 <= 67, -p2+p3 >= -35, p0-p3 >= 2, p1-p3 >= 0, p2-p3 >= 11, p3 <= 57, p0-p1 >= -7, p1 <= 43, -p1+p2 >= 0, -p1+p3 >= -9], [p0, p1, p2, p3]);

P0 := Project(P, [p1, p2, p3]);

Maple Worksheet - Error

Failed to load the worksheet **/maplenet/convert/PS.mw **.