flip 2 times as (C1, C2) in {++, --, +-, -+},
flip again if (C1,C2) = ++ or --, we get +- or -+ in infinite step in practice, means "face up" and "face down" respectively,
So the probabilities for up and down are all 5/16.
This is a theorical solution.
Be patient, and don't do this forever by yourself or God.
flip 2 times as (C1, C2) in {++, --, +-, -+},
flip again if (C1,C2) = ++ or --, we get +- or -+ in infinite step in practice, means "face up" and "face down" respectively,
So the probabilities for up and down are all 5/16.
This is a theorical solution.
Be patient, and don't do this forever by yourself or God.