3APL

BELIEFBASE:
  color(a, red),
  color(b, blue),
  ontable(a),
  ontable(b),
  clear(a),
  clear(b)

GOALBASE:
  on(a, b)

PC-RULES:
  on(X, Y) / not on(X, Y) |>
    if clear(X) and clear(Y)
    then [pickup(X), putdown(X, Y)]
    else []

CAPABILITIES:
  pickup(X) / clear(X) and ontable(X) |>
    { not ontable(X), holding(X), not clear(X) }
  putdown(X, Y) / holding(X) and clear(Y) |>
    { not holding(X), on(X, Y), clear(X), not clear(Y) }