+
+definition Qtimes : Q \to Q \to Q \def
+\lambda p,q.
+ match p with
+ [OQ \Rightarrow OQ
+ |Qpos p1 \Rightarrow
+ match q with
+ [OQ \Rightarrow OQ
+ |Qpos q1 \Rightarrow Qpos (rtimes p1 q1)
+ |Qneg q1 \Rightarrow Qneg (rtimes p1 q1)
+ ]
+ |Qneg p1 \Rightarrow
+ match q with
+ [OQ \Rightarrow OQ
+ |Qpos q1 \Rightarrow Qneg (rtimes p1 q1)
+ |Qneg q1 \Rightarrow Qpos (rtimes p1 q1)
+ ]
+ ]
+.
+
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