OQ, TH meet at P. We must prove that AC also passes thro P
If OT = R and QH = r, then OA = sqrt2 R and QC = sqrt2 r
So OA/QC = OT/QH which in turn = PO/PQ
Now consider the right triangles POA and PQC in which PO/PQ = OA/QC and < O < Q = 90
It follows that the 2 right triangles are similar and so < PAO =PCQ and for this to happnd PCA must be collinear
Hence AC, OQ and TH meet in a point P