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Step * of Lemma arctangent1

arctangent(r1) = (π/r(4))
BY
{ Assert ⌜(π/r(4)) ∈ {x:ℝ| (-(π/2) < x) ∧ (x < π/2)} ⌝⋅ }

1
.....assertion..... 
(π/r(4)) ∈ {x:ℝ| (-(π/2) < x) ∧ (x < π/2)} 

2
1. (π/r(4)) ∈ {x:ℝ| (-(π/2) < x) ∧ (x < π/2)} 
⊢ arctangent(r1) = (π/r(4))

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Latex:

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Latex:
arctangent(r1)  =  (\mpi{}/r(4))


By

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Latex:
Assert  \mkleeneopen{}(\mpi{}/r(4))  \mmember{}  \{x:\mBbbR{}|  (-(\mpi{}/2)  <  x)  \mwedge{}  (x  <  \mpi{}/2)\}  \mkleeneclose{}\mcdot{}

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