Misc fixes

[skirpichev]

No description provided.

[skirpichev]

@sylee957, maybe it could be interesting to you. It seems, either eval() error in the sympy/sympy#20484 is fixed in the Diofant or it's a regression.

Also, you may do that you want with poly_subs() by existing .compose() method:

In [24]: R, x, y, z = ring('x y z', ZZ)

In [25]: f = x*y*z

In [26]: f.compose(x, y*z)
Out[26]: y**2*z**2

In [27]: _26.ring
Out[27]: ℤ[x, y, z]

In [28]: f.compose(x, y*z).drop(x)
Out[28]: y**2*z**2

In [29]: _28.ring
Out[29]: ℤ[y, z]

In [33]: R, x, y = ring('x y', QQ)

In [34]: f = x**2 + 1

In [35]: f.compose(x, x + y)
Out[35]: x**2 + 2*x*y + y**2 + 1

(For FractionField's this is not implemented yet either in the SymPy or the Diofant. I'll, probably, fix this in the current PR.)

[skirpichev]

#961 seems to be also relevant here.