Under the leadership of Einstein's SRT:

t'=(t-V/c x/c)/Sqrt(1-Sqr(V/c))
t=(t'+V/c x'/c)/Sqrt(1-Sqr(V/c))

x'=(x-Vt)/Sqrt(1-Sqr(V/c))
x=(x'+Vt')/Sqrt(1-Sqr(V/c))
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As cited from "General Physics I"
SBN: 9989-43006-3
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The hack:
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x'/t = (x-Vt)/(t'+V/c x'/c) and
x/t' = (x'+Vt')/(t-V/c x/c) ==>
x't'+VSqr(x'/c) = xt-vt^2 and
xt-VSqr(x/c)=x't'+Vt'^2 ==>

x't'-xt=-V(Sqr(x'/c)-t^2) and
x't'-xt=-V(Sqr(x/c)-t'^2) ==>

-(x't'-xt)/V=(t^2+Sqr(x'/c)) and
-(x't'-xt)/V=(t'^2+Sqr(x/c)) ==>

t^2+Sqr(x'/c)=t'^2+Sqr(x/c) ==>

(t-t')(t+t')=(x-x')/c (x+x')/c

V=x/t=c and V'=x'/t'=c

Conclusion: Every speed is speed of light!
Einstein hacked! Bring in the next therorist!