procedure main(A)
    if2 { (A[1] = A[2]), (A[3] = A[4]),   # Use PDCO with all three else clauses
          write("1: both true"),
          write("1: only first true"),
          write("1: only second true"),
          write("1: neither true")
        }
    if2 { (A[1] = A[2]), (A[3] = A[4]),    # Use same PDCO with only one else clause
          write("2: both true"),
          write("2: only first true"),
        }
end

procedure if2(A)		# The double-conditional PDCO
    suspend if @A[1] then
        if @A[2] then |@A[3]    # Run-err if missing 'then' clause
        else @\A[4]	        # (all else clauses are optional)
    else if @A[2] then |@\A[5]
    else |@\A[6]
end