How to construct a product of a-frames

Douglas S. Bridges. How to construct a product of a-frames. Math. Log. Q., 58(4-5):281-293, 2012. [doi]

@article{Bridges12-0,
  title = {How to construct a product of a-frames},
  author = {Douglas S. Bridges},
  year = {2012},
  doi = {10.1002/malq.201110059},
  url = {http://dx.doi.org/10.1002/malq.201110059},
  researchr = {https://researchr.org/publication/Bridges12-0},
  cites = {0},
  citedby = {0},
  journal = {Math. Log. Q.},
  volume = {58},
  number = {4-5},
  pages = {281-293},
}