From
毛泽东 《七律·长征》 ('Seven-character regulated verse: The Long March,' 1935):
红军不怕远征难,
万水千山只等闲 ... The
暖 (warm) /
寒 (cold) contrast tracks the two river crossings - Jinsha was a success, Dadu a near-disaster. Written soon after the Red Army completed the 1934-35 Long March.