$ P$$ BC$$ ABC$$ AP \neq AB,AP \neq AC$$ l_1,l_2$$ ABP,ACP$$ W_1,W_2$$ l_1,l_2$$ l_1P,l_2P$$ W_1,W_2$$ P$$ Q$$ W_1$$ AB$$ BC$$ Y_1( \mbox{the intersection closer to B})$$ X_1$$ W_2$$ AC$$ BC$$ Y_2(\mbox{the intersection closer to C})$$ X_2$$ PQ,X_1Y_1,X_2Y_2$