from functools import reduce


def get_eqns_unk (eqns, knowns):
    """Returns the list of unknowns, given the knowns, from a list of equations"""
    if not isinstance(eqns, (list, tuple)):
        eqns = [eqns]
    atoms = reduce(lambda acc, eqn: acc.union(eqn.atoms()), eqns, set())
    return filter(lambda x: not x.is_Number, atoms - set(knowns))