If its argument is a pure scalar clifford object, or the pseudoscalar,
coerce to numeric. Scalar or pseudoscalar clifford objects are
coerced to an unnamed numeric vector (of length 1). Checking
for being the pseudoscalar requires that option maxdim
be set.
Function drop()
is generic, dispatching to helper function
drop_clifford()
for clifford objects. The logic of
drop_clifford()
prevents is.pseudoscalar()
being called
if maxdim
is NULL
.