 The random variable "y"("t") is the observation at time (with "y"("t") ∈ { "y"1, "y"2, "y"3, "y"4 }).The arrows in the diagram (often called a trellis diagram) denote conditional dependencies.From the diagram, it is clear that the conditional probability distribution of the hidden variable "x"("t") at time , given the values of the hidden variable at all times, depends "only" on the value of the hidden variable "x"("t" − 1); the values at time "t" − 2 and before have no influence.