...expressions.
Not to be confused with Woodcock and Loomes's use of tex2html_wrap_inline209 for tex2html_wrap_inline213 . 
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... tex2html_wrap_inline287 .
The symmetry property says that we can do the proof backwards. Notice that if = were replaced by tex2html_wrap_inline319 we could not do that! 
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...before.
It's also possible to reduce both sides of the equation at the same time, but since you'd really be doing two proof steps simultaneously, you need to be careful to justify both steps. We do not recommend this procedure. 
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Norman Papernick
Fri Mar 15 12:00:46 EST 1996