qepcad fails to find an existing solution

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I've been trying to use qepcad on the Sagecell and I have the following problem. If I run the following code:

var('a1, a2, a3, a4, d1, d2, d3, d4')

qf = qepcad_formula

F1 = qf.and_( a1 >= 1, a2 >= 1, a3 >= 1, a4 >= 1, d1 >= 0, d2 >= 0, d3 >= 0, d4 >= 0, a1*d1 + a2*d2 + a3*d3 - a4*d4 == 0, d1 + d2 < d3 + d4 )

qepcad(F1, solution = 'any-point')

Then I get a possible solution with {... 'd4' : 1}. However if I perform nearly the same computation, except with the condition d4 >= 0 changed to d4 >= 1, then I get an error:

var('a1, a2, a3, a4, d1, d2, d3, d4')

qf = qepcad_formula

F2 = qf.and_( a1 >= 1, a2 >= 1, a3 >= 1, a4 >= 1, d1 >= 0, d2 >= 0, d3 >= 0, d4 >= 1, a1*d1 + a2*d2 + a3*d3 - a4*d4 == 0, d1 + d2 < d3 + d4 )

qepcad(F2, solution = 'any-point')

which gives ... ValueError: input formula is false everywhere. However the solution to the first example is a valid solution to the second example so I'm not sure what's going on.

Any help would be greatly appreciated!