Redefine `function'. Now cl21:function also can take a list.

Example:
  (function integerp) => #'integerp
  (function (and integerp zerop)) => (conjoin #'integerp #'zerop)
  (function (and integerp (or evenp zerop))) => (conjoin #'integerp (disjoinp #'evenp #'zerop))

  (funcall (function (and integerp zerop)) 0) => T
  (funcall (function (and integerp zerop)) 0.0) => NIL
  (funcall (function (and integerp zerop)) 0.0) => NIL
  (funcall (function (and integerp (or evenp zerop))) 0) => T
  (funcall (function (and integerp (or evenp zerop))) 1) => NIL
  (funcall (function (and integerp (or evenp zerop))) 2) => T
Stop using #' for papply and replace it by cl21.core.function:function. `papply' looks very useful but cl21.core.function:function is more natural.
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