Bug with variable names in solve()

[tastalian]

Some variable names yield strange behavior with the solve() function. Here is an example:

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| Sage Version 4.4.2, Release Date: 2010-05-19                       |
| Type notebook() for the GUI, and license() for information.        |
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sage: var('d2 d3 x')
(d2, d3, x)
sage: solve((d2+d3)*x==1, x)
[x == factorial(2*k + 6*n)/(d3*factorial(2*k + 6*n) + factorial(k + 3*n - 1))]

These factorials are strange. They don't occur with other variable names, e.g.,

sage: var('y1 y2 x')
(y1, y2, x)
sage: solve((y1+y2)*x==1, x)
[x == (1/(y1 + y2))]

Documentation for solve() does not mention reserved variable names.

[mhansen]

This is basically a duplicate of #8734.