Desmaison began climbing in Fontainbleau as part of the third generation of young Parisian mountaineers and climbers known as the "Group of Bleau." There, in 1954, he met Jean Couzy, a young aerospace engineer and test pilot, with whom he climbed extensively in the Alps, particularly on the west face of the Petit Dru. He made the fourth ascent of the Dru's original route, as well as both the first winter ascent and the first solo ascent of the same route. With Couzy, who died tragically in 1958, he added also a new line--the all time third--on the Marguerite spur of north face of the Grandes Jorasses.
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