Published online by Cambridge University Press: 20 November 2018
A magma  $\left( M,\star\right)$  is a nonempty set with a binary operation. A double magma
 $\left( M,\star\right)$  is a nonempty set with a binary operation. A double magma  $\left( M,\star ,\bullet\right)$  is a nonempty set with two binary operations satisfying the interchange law
 $\left( M,\star ,\bullet\right)$  is a nonempty set with two binary operations satisfying the interchange law  $\left( w\star x \right)\bullet \left( y\star z \right)=\left( w\bullet y \right)\star \left( x\bullet z \right)$ . We call a double magma proper if the two operations are distinct, and commutative if the operations are commutative. A double semigroup, first introduced by Kock, is a double magma for which both operations are associative. Given a non-trivial group
 $\left( w\star x \right)\bullet \left( y\star z \right)=\left( w\bullet y \right)\star \left( x\bullet z \right)$ . We call a double magma proper if the two operations are distinct, and commutative if the operations are commutative. A double semigroup, first introduced by Kock, is a double magma for which both operations are associative. Given a non-trivial group   $G$  we define a system of two magma
 $G$  we define a system of two magma   $\left( G,\star ,\bullet\right)$  using the commutator operations
 $\left( G,\star ,\bullet\right)$  using the commutator operations   $x\star y=\left[ x,y \right]\left( ={{x}^{-1}}{{y}^{-1}}xy \right)$  and
 $x\star y=\left[ x,y \right]\left( ={{x}^{-1}}{{y}^{-1}}xy \right)$  and   $x\bullet y=\left[ y,x \right]$ . We show that
 $x\bullet y=\left[ y,x \right]$ . We show that   $\left( G,\star ,\bullet\right)$  is a double magma if and only if
 $\left( G,\star ,\bullet\right)$  is a double magma if and only if   $G$  satisfies the commutator laws
 $G$  satisfies the commutator laws   $\left[ x,y;x,z \right]=1$  and
 $\left[ x,y;x,z \right]=1$  and   ${{\left[ w,x;y,z \right]}^{2}}=1$ . We note that the first law defines the class of 3-metabelian groups. If both these laws hold in
 ${{\left[ w,x;y,z \right]}^{2}}=1$ . We note that the first law defines the class of 3-metabelian groups. If both these laws hold in   $G$ , the double magma is proper if and only if there exist
 $G$ , the double magma is proper if and only if there exist   ${{x}_{0}},{{y}_{0}}\in G$  for which
 ${{x}_{0}},{{y}_{0}}\in G$  for which   ${{\left[ {{x}_{0}},{{y}_{0}} \right]}^{2}}\ne 1$ . This double magma is a double semigroup if and only if  
 $G$  is nilpotent of class two. We construct a specific example of a proper double semigroup based on the dihedral group of order 16. In addition, we comment on a similar construction for rings using Lie commutators.
 $G$  is nilpotent of class two. We construct a specific example of a proper double semigroup based on the dihedral group of order 16. In addition, we comment on a similar construction for rings using Lie commutators.