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The Gill " B " system The B-System conceived by John Gill in the 1950s was a universal rating scheme for bouldering , having three categories : " B1 " was defined as " ... the highest level of difficulty in traditional roped climbing " , " B2 " was harder than B1 , or " bouldering level " , and the grade " B3 " designated a route ascended only once , although tried by others on several occasions .
 Gill, John Gill
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 Gill, John Gill