A method of processing video data, comprising: determining, for a conversion between a block of a current picture of a video and a bitstream of the video, that a first coding mode is applied to the block based on a derivation process of two target reference pictures of the current picture, wherein the conversion includes decoding the block of the video from the bitstream or encoding the block of the video into the bitstream, wherein the derivation process includes: performing a first step for searching a forward target reference picture in a reference picture list 0 and searching a backward target reference picture in a reference picture list 1, in response to at least one of the two target reference pictures being not found in the first step, resetting both the target reference picture indices to be unavailable before a second step being invoked, wherein resetting both the target reference picture indices to be unavailable comprises resetting both RefIdxSymL0 and RefldxSymL1 to -1, wherein RefIdxSymL0 indicates the target reference picture index in the reference picture list 0 and RefldxSymL1 indicates the target reference picture index in the reference picture list 1, and performing the second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1; and performing the conversion based on the determination, wherein in the first coding mode, a syntax structure indicating a motion vector difference of a reference picture list X is not present in the bitstream, and the motion vector difference of the reference picture list X is derived based on a motion vector difference of a reference picture list (1-X), wherein X is equal to 0 or 1. determining, for a conversion between a block of a current picture of a video and a bitstream of the video, that a first coding mode is applied to the block based on a derivation process of two target reference pictures of the current picture, wherein the conversion includes decoding the block of the video from the bitstream or encoding the block of the video into the bitstream, wherein the derivation process includes: performing a first step for searching a forward target reference picture in a reference picture list 0 and searching a backward target reference picture in a reference picture list 1, in response to at least one of the two target reference pictures being not found in the first step, resetting both the target reference picture indices to be unavailable before a second step being invoked, wherein resetting both the target reference picture indices to be unavailable comprises resetting both RefIdxSymL0 and RefldxSymL1 to -1, wherein RefIdxSymL0 indicates the target reference picture index in the reference picture list 0 and RefldxSymL1 indicates the target reference picture index in the reference picture list 1, and performing the second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1; and performing a first step for searching a forward target reference picture in a reference picture list 0 and searching a backward target reference picture in a reference picture list 1, in response to at least one of the two target reference pictures being not found in the first step, resetting both the target reference picture indices to be unavailable before a second step being invoked, wherein resetting both the target reference picture indices to be unavailable comprises resetting both RefIdxSymL0 and RefldxSymL1 to -1, wherein RefIdxSymL0 indicates the target reference picture index in the reference picture list 0 and RefldxSymL1 indicates the target reference picture index in the reference picture list 1, and performing the second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1; and performing the conversion based on the determination, wherein in the first coding mode, a syntax structure indicating a motion vector difference of a reference picture list X is not present in the bitstream, and the motion vector difference of the reference picture list X is derived based on a motion vector difference of a reference picture list (1-X), wherein X is equal to 0 or 1.