L-erythrulose 1-phosphate <=> D-erythrulose 4-phosphate
l-erythrulose 1-phosphate <=> d-erythrulose 4-phosphate
L-erythrulose 1-phosphate <=> D-erythrulose 4-phosphate
l-erythrulose 1-phosphate <=> d-erythrulose 4-phosphate