Quaternion can't use subs ?

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Hi

we can't use subs with quaternions?

Q.<i,j,k> = QuaternionAlgebra(SR, -1, -1)
aVars = var('a', n=4, latex_name='a')
bVars = var('b', n=4, latex_name='b')
qa = a0 + a1 * i + a2 * j + a3 * k
dic={a0: -1, a1: 0, a2: 1, a3: 0}
print(qa.substitute(dic))
eq=[a0==-1,a1==0,a2==1,a3==0]
print(qa.subs(eq))