[(x⊃y) · (z·x)]
/∴ (x·y) · z

1. (z·x), you simplify
2. x
3. z
(more simply)
4. x⊃y, you simplify
5. y, by 2 and 4, MP
6. x·y, by 2 and 5
7. (x·y) · z, by 6 and 3
QED



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TRANSCRIBED:
If ‘x’ then ‘y’ and ‘z’ and ‘x’
it follows that ‘x’, and ‘y’, and ‘z’.
One, ‘z’ and ‘x’ – you simplify.
Two, ‘x’;
three, ‘z’
more simply.
Four: ‘x’, then ‘y’, you simplify.
Five: ‘y’ by two and four M.P.
Six: ‘x’ and ‘y’, by two and five.
Seven: ‘x’ and ‘y’, and ‘z’ by six and three.
Q.E.D.