## mark a section (Learn more)

irb(main):010:0> a = [1, 2] => [1, 2] irb(main):012:0> m = Matrix[a] => Matrix[[1, 2]] irb(main):013:0> m2 = m.clone => Matrix[[1, 2]] irb(main):014:0> a << 3 => [1, 2, 3] irb(main):015:0> m => Matrix[[1, 2, 3]] irb(main):016:0> m2 => Matrix[[1, 2]] irb(main):017:0>

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