Magic determinants of Somos sequences and theta functions

By means of an almost trivial statement of matrix algebra, we prove two conjectures proposed by Gosper and Schroeppel [R.W. Gosper, R. Schroeppel, Somos sequence near-addition formulas and modular theta functions, arXiv:math.NT/0703470v1, 15 March 2007.] on near-addition formulas for 4- and 5-Somos sequences. A simplified proof for an elliptic analogue of this conjecture recently shown by Cooper and Toh in [S. Cooper, P.C. Toh, Determinant identities for theta functions, J. Math. Anal. Appl. 347 (2008) 1–7] is also presented.