One important feature of this exploration policy is that the objective function (i.e., overall barrier) of each node are updated after each stage of exploration. This creates the possibility of backtracking to a node, (e.g., nodes previously considered as inaccessible are selected for exploration when low-barrier pathways connecting them are discovered or when downstream nodes prove to have higher overall barriers). A typical example is 3-hexulose (7-6 in Fig. ), which was discovered during the second step of the exploration process, but was not considered a relevant intermediate for exploration until the seventh step of exploration. The overall barrier for 3-hexulose was updated from 39.62 (at depth 2) to 37.01 (at depth 3) and finally to 30.98 (at depth 6) due to the discovery of a low-barrier conversion from node 6-2, catalyzed by multiple hydroxyl groups (an important reaction mechanism discussed later in section 2. species can convert into a more stable isomer, dihydroxyacetone (DHA, node 5-4), through watercatalyzed keto-enol tautomerization reactions. Besides, glyceraldehyde can decompose into HAA through a retro-aldol reaction and a keto-enol tautomerization. HAA and DHA, being more stable compared with other isomers, act as two thermochemical sinks in this sub-network, providing an explanation for the experimental observation of these two products even apart from the detailed analysis considered in the subsequent sections.