I have:
equaz = {-4 + y == 0, 13 + 5 x + 3 y == 0, 23 + 7 x + 3 y == 0, 9 + 5 x - y == 0, 11 + 7 x - y == 0, 2 + x == 0, -1 + 7 x + 9 y == 0, 5 + x + 3 y == 0, 3 + y == 0, 3 + 7 x + y == 0, 3 + x + y == 0}
why, if I type in an explicit form, it works and if I type the reference "equaz", it does not work?
ContourPlot [{-4 + y == 0, 13 + 5 x + 3 y == 0, 23 + 7 x + 3 y == 0, 9 + 5 x - y == 0, 11 + 7 x - y == 0, 2 + x == 0, -1 + 7 x + 9 y == 0, 5 + x + 3 y == 0, 3 + y == 0, 3 + 7 x + y == 0, 3 + x + y == 0}, {x, -20, 30}, {y, -20, 30}]
-> work
ContourPlot [equaz, {x, -20, 30}, {y, -20, 30}]
-> don't work, white graph
tnk's